The present invention relates to a powder of a rare earth oxide or, more particularly, to a powder of a rare earth oxide capable of giving greatly increased stability to the consistency of an aqueous slurry of the powder for shaping or molding of a green ceramic body as well as to a method for the preparation of such an improved rare earth oxide powder as well as a green ceramic body shaped from such a rare earth oxide powder.
As is well known, rare earth oxide powders are widely used as a material of various kinds of ceramic articles such as crucibles, base plates used in a high-temperature treatment of other articles as well as a coating material of various kinds of ceramic articles by virtue of the very excellent properties thereof as a refractory material. When a rare earth oxide powder is used in these applications, a procedure which is undertaken almost always is that the rare earth oxide powder is blended with and dispersed in a certain volume of water to make a slurry of the powder having an adequate consistency depending on the particular method for shaping or molding of a green ceramic body or for coating to form a covering layer on a substrate ceramic body.
A serious problem in such an aqueous slurry of a rare earth oxide powder is that aqueous slurries of a rare earth oxide powder are usually unstable in the consistency in the lapse of time to cause an increase of the consistency within a relatively short time due to the reactivity of the rare earth oxide particles with water. Accordingly, it is necessary in the prior art that an aqueous slurry of a rare earth oxide powder is prepared immediately before each time of the use of the slurry for shaping green ceramic bodies or before the use of the slurry as a coating material. This problem can of course be mitigated by decreasing the content of the rare earth oxide powder in the aqueous slurry or by admixing the aqueous medium of the slurry with a water-miscible organic solvent. The former method is of course not practical because of the decrease in the productivity of the manufacturing process of rare earth oxide-based ceramics if not to mention that certain molding methods cannot be applied to an aqueous slurry of such a decreased content of the oxide powder. The latter method is also not practical because the use of an organic solvent always involves problems relative to the health and safety of workers and environmental pollution caused by the waste water containing an organic solvent if not to mention an increase in the costs for the dispersion medium.